1. Field of the Invention
The present invention relates to a measuring device for controlling an installation torque of a fastening element, in particular, for controlling an installation torque of a dowel, a screw or the like and securable to the engagement means of the fastening element. The measuring device has an opening through which a fastening element can extend and includes an indicator for a visual display of the installation torque, and a plurality of microcapsules supported on the indicator. The microcapsules are filled with at lest one dispersible color die. The present invention further relates to a fastening system including a fastening element, in particular, a dowel, a screw or the like, and a measuring device.
2. Description of the Prior Art
For controlling a torque applied to a fastening element, e.g., a dowel and the like, the engagement means of the fastening element, e.g., a screw head of a dowel, can be provided, e.g., with a breakable cap that breaks at a certain load. The breakable caps are generally expensive and their manufacturing is associated with noticeable costs.
A drawback of the control mechanism, which uses breakable caps or the like, consists in that they indicate only the instantaneous torque applied to a fastening element. It is more important, however, to control the pre-stressing force of a fastening element.
U.S. Pat. No. 3,948,141 discloses a load indicating washer provided with an insert or a microcapsule with a color material that is pressed out sidewise under a certain load.
German Utility Model DE 78 21 489U1 discloses a load indicating washer in which for a better sidewise release of the inserted material, there are provided outlet channels extending up to the outer circumference of the washer.
U.S. Pat. No. 6,425,718 discloses a washer having indentations with different depths and filled with extrudable color materials. Upon tightening of a bolt, under a compression force, the colored material is extruded sidewise. The degree of the applied tension is determined by the color of the extruded material.
The drawback of the known solutions consists in that the sidewise extrudable color material can soil a visible region of a fastening element. Besides, the inserted material can change its characteristics under external influences, e.g., become brittle, which would not insure a precise determination of the tension applied to a fastening element. Moreover, the known solutions are applied, primarily, only to one type of a fastening element.
Accordingly an object of the present invention is to provide a measuring device that would insure a high precision of a visual control of the tension applied to a fastening element.
Another object of the present invention is to provide a measuring device that can be universally used and cost-effectively manufactured.
A further object of the present invention is to provide a measuring device the elements of which would not soil the visible region of a fastening element.